1. Field of Invention
The present invention relates to a method and apparatus for chemically treating thin materials.
2. Description of the Prior Art
In the field of wet processing, particularly that of treatment of printed circuit boards and industrial parts, the boards are often treated by wave soldering, etching, cleaning or the like, followed by various other treatments, generally including as a minimum, rinsing and drying. Similarly, in other types of treatments, such as electroplating or the like, the articles or items being plated are likewise followed by subsequent treatment steps, such as rinsing, drying and the like.
In the electronics industry, the art has developed progressively thinner printed circuit boards to the extent that the rigid or semi-ridged printed boards have become increasingly thinner and approach or become more of a flexible film. The processing of such "boards", which can more precisely resemble films, presents new concerns in the handling of these articles, as the thin materials have a tendency to buckle and cause jamming of the treatment or processing apparatus. This is especially the case where the circuit board material comprises a thin film and where a liquid treatment tends to accumulate on the board and weigh it down as it is being moved along the apparatus. In some cases additional supports have been provided on an apparatus to retain the film in place as it travels through a processing area or treatment center. One attempt to deal with this problem is shown in U.S. Pat. No. 4,781,205, the complete disclosure of which is herein incorporated by reference, wherein an arrangement of several fixedly disposed bands at staggered positions along the transport means are utilized. In addition, U.S. Pat. No. 5,176,158, the complete disclosure of which is herein incorporated by reference, supports thin circuit boards with guide wires which are moved back and forth as the circuit board or article is being transported.
However, in some instances, the presence of additional elements masks areas of the board to be treated from the treatment process, and such additional elements may prevent the removal of residues of the treatment process in a cleaning operation, such as, for example, rinsing with water which may be done to remove excess treatment chemicals.
Other transport methods known in the prior art include contacting boards with a series of thin cylindrical wheels. In such prior art applications, each wheel often includes a circumferential surface which continually contacts a board over a single linear longitudinal path across a board's surface. This permits the possibility for fluid treatment buildup on lateral sides of the board area lying between adjacent wheels, and differences in amount of treatment that a board sees can occur, resulting in longitudinal bands of differential treatment. Also, as thinner boards (film) are transported by such thin wheels, the boards can bow in zones between wheels, thereby accumulating puddles of treatment liquid on the boards in the troughs formed on the boards between wheels. The build-up of solution on the boards is a compounding effect, since as more solution accumulates on the board, the board, absent support, is increasingly made more susceptible to buckling. The buckling creates a greater reservoir for yet additional treatment fluid to be taken up, thereby weighing down the film or board.
Attempts have been made to provide fingers or whiskers extending from a wheel for additional support of articles. However, the fingers must be spread out from one another to permit treatment administration. This can permit treatment liquid to build up on a board. In addition, there is still a linear path of differential treatment made by the wheel to which the fingers are attached.